Fix drift counts from runner group inventory

[jmcte]

Summary

• count drift inventory from each runner group runners endpoint instead of relying on org-wide runner_group_id fields
• record the current selected public runner-group repository access, including apw-cli
• keep drift output aligned with GitHub's current org runner API behavior

Verification

• pnpm exec vitest run test/drift-detect.test.ts test/cli.test.ts test/github.test.ts test/config.test.ts
• pnpm validate-config -- --config config/pools.yaml --env .env
• pnpm validate-github -- --config config/pools.yaml --env .env
• GITHUB_PAT= pnpm drift-detect -- --config config/pools.yaml --threshold 0 now reports synology-private actual=4 and synology-public actual=2

[pheidon]

Pheidon pass: reviewed diff and green checks look good. Approving.

[pheidon]

@daedalus-omt quick nudge from the Pheidon pass: this PR is approved on my side and auto-merge is enabled. If you still need to review, please do; if the request is stale, please clear it so this can land cleanly.